The use of silicones in hair treatment compositions is well known and widely documented in the patent literature. Generally, dispersed droplets of silicone are suspended in the composition, which is then applied to the hair to deposit the material on the hair shaft.
Hitherto, steps have had to be taken to prevent the emulsified droplets of silicone oil from agglomerating and the composition creaming during storage. Such steps have for example included the addition of polymers such as Carbopol or certain gums, and/or crystalline materials, to act as suspending agents, but the use of such materials renders the resulting compositions cloudy or opaque, which is a problem if it is desired to formulate optically clear compositions.
The presence of such suspending agents in hair treatment compositions, however, is also disadvantageous because they can lead to dulling of the hair, as well as lowering of other conditioning attributes, as a result of the suspending agent being deposited on the hair in addition to the intended silicone conditioning oil.
It is known in the art that oily cosmetic agents such as silicones can be incorporated into cosmetic compositions by means of microemulsification, whereby the silicone is present as stably emulsified droplets of a particle size of the order of 0.15 microns or less.
For example, U.S. Pat. No. 4 733 677 discloses leave-on hair fixatives containing cationic organic polymer and polydiorganosiloxane microemulsion. EP A 268 982 describes dimethylpolysiloxane microemulsions for various cosmetic uses, the microemulsified dimethylpolysiloxane being formed by emulsion polymerisation and with a particle size of 0.15 microns or less.
In EP A 0 529 883 there is disclosed a hair shampoo comprising a silicone microemulsion in combination with a cationic deposition polymer. This shampoo has good mechanical stability and high optical transparency or translucency since a suspension system is not required to stabilise the microemulsified particles of silicone.
The silicone microemulsion used in EP A 0 529 883 has a particle size of 0.036 microns and a viscosity of 15,000 centistokes. EP A 0 674 898 discloses how the use of higher viscosity microemulsion in such a system improves the conditioning performance. The viscosity of the microemulsion used here is 60,000 centistokes.
A problem is that even the higher viscosity microemulsion disclosed in EP A 0 674 898 does not give a sufficient conditioning benefit for many people.
We have now found that shampoo compositions having excellent mechanical stability and conditioning ability can be obtained by utilising microemulsions of silicone in which the silicone is very slightly cross-linked in the emulsion form. Neither EP A 0 529 883 nor EP A 0 674 898 make any mention of the silicone microemulsion being cross-linked.